Best Body for AF Tracking

Any thoughts on the best body specifically for AF Tracking? I had a G3 last year which was reasonable, but after a short dip into full-frame Canon shooting I'm coming back to M4/3 and I'm a bit out of touch.

It needs to be a DSLR-like body as it's for motorsport shooting with the 100-300 (and probably 35-100).

I'm guessing OMD or G5? I would just go straight for the OMD, but it's double the price (£1000 vs £500) here in the UK at the moment, so it would have to be significantly better to warrant a purchase.